Rewilding

Allowing (and/or encouraging) land (and water, such as ocean beds) that was formerly used for agriculture (and other human activities) to transform to states determined more by natural processes, can increase sequestration of Carbon in plants and soils and increase biodiversity of plant and animal populations. Sometimes this rewilding happens of its own accord when land once used by humans is simply abandoned, for example woodlands that were once used to supply firewood were no longer needed for this when people switched to using coal.
Research[1]
suggests that the genocide of native American people by European immigrants at the end of the 15th century led to rewilding of agricultural land which drew down carbon causing global cooling, resulting in the
"little ice age".
A relatively recent example is the Chernobyl exclusion zone which is now "arguably a nature reserve", rich in wildlife since most humans evacuated from the area in 1986.

Deliberate rewilding often involves human intervention to influence the course of change, such as deliberate reforestation, and the introduction of top predators such as wolves, or culling large herbivores such as deer, to allow trees to grow.

The IPCC in its Special Report on Climate Change and Land examines the relationships between "climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems".

Biologist E. O. Wilson has suggested that we should aim to set aside half of the world's land surfaces for wildlife.[2][3]

Contents

Arctic

A 2020 paper from the University of Oxford suggests the wide-scale introduction of large herbivores to the Arctic tundra to restore the ‘mammoth steppe’ grassland ecosystem and mitigate global warming:[4]

Grazing animals such as horses and bison are known to engineer the landscape around them, for example suppressing the growth of trees by trampling or eating saplings. When this process is harnessed to restore an ecosystem to a previous state it is called rewilding. It can also be used to change one ecosystem into a different but more desirable state. This is referred to as megafaunal ecosystem engineering.

In many parts of the world, forest ecosystems are considered the most important to restore due to their ability to store carbon. But in the Arctic tundra shifting the landscape from woody vegetation to grassland would enhance the protection of the carbon-rich permafrost, reduce carbon emissions associated with permafrost thaw and increase carbon capture in the soil.

This grassland ecosystem – called the ‘mammoth steppe’ – existed during the Pleistocene period, but was lost when large herbivores such as woolly mammoths went extinct. Horses and bison could act as eco-engineers to transform present day tundra back to grassland. By removing woody vegetation, enhancing grass growth, and trampling on snow in search of winter forage, large mammals increase the amount of incoming solar energy that bounces back to space – known as albedo. Grasslands also favour the capture of carbon in the deep roots of grasses, and enable cold winter temperatures to penetrate deeper into the soil. Altogether, these changes would have a net cooling effect on Arctic lands and delay permafrost melt.

“The Arctic is already changing, and fast. Taking a ‘do nothing’ approach now is a decision to allow rapid, irreversible changes to occur,” says lead author Dr Marc Macias-Fauria, head of the Biogeosciences Group at the School of Geography & the Environment. “Although the science of Arctic eco-engineering is largely untested, it has the potential to make a big difference and action in this region should be given serious consideration.”

The Oxford-led study estimates that carbon emissions from thawing permafrost could be around 4.35 billion metric tonnes per year over the 21st century. This is around half as much as fossil fuels emissions and three times more than estimates of the emissions produced by current and projected land use change.

“Considering land use strategies aimed at protecting the Arctic permafrost has similar implications for climate change as land use decisions in other regions which currently receive much more attention,” explained Professor Yadvinder Malhi, leader of the Ecosystems Group at the Environmental Change Institute. “We are not used to thinking about the Arctic in this way.”

The Pleistocene Park, a family-run grassland restoration project currently operating in north-easternmost Russia, has already shown promising results. But the paper highlights that the scale of animal introductions needed to have a significant impact on Arctic tundra and therefore global climate poses a significant challenge. As a starting point there is now a need for large experiments at the interface of science and practice.

The fossil record has been used to estimate that in the Pleistocene, 1 mammoth, 5 bison, 7.5 horses, 15 reindeer, 0.25 cave lions, and 1 wolf per square kilometre roamed the area – around the animal density of present-day African savanna game reserves. Rewilding efforts would initially focus on bison and horses. Researchers cost the introduction and monitoring of three large-scale experimental areas consisting of 1,000 animals each at US$114 million over a period of 10 years. On a yearly basis, these areas would be able keep up to 72,000 tonnes of carbon in the ground and generate US$360,000 in carbon revenues alone, increasing once the research phase was conducted and scaling enabled more cost-efficient practices. Returns could be significantly higher if Arctic countries introduced carbon tax and pricing mechanisms, and the study constitutes a potential opportunity for UK-Russia cooperation on climate change mitigation. The logistics, costs and social considerations necessary to rewild the Arctic would be a monumental task – but the climate payoff could be mammoth.

Eco-engineering is one example of a natural climate solution, part of the wider framework of ‘nature-based solutions’. The concept of nature-based solutions broadly refers to working with and enhancing nature to help address societal challenges, and is rapidly gaining traction around the world.

Megafauna

Why is it possible to lay a hedge? In other words, why did trees evolve to survive the mangling that traditional hedgelayers inflict on them? They almost sever the living wood, twist it, split it and trample it down. Yet, the trees bounce back, as lively as before. Why do most deciduous trees in Britain and Europe coppice and pollard: resprout from wherever the trunk is broken? Why do birch trees have black and white bark? Why do understorey trees, like box and holly and yew, have tougher roots and branches than big canopy trees, such as oak and beech and lime, though they carry less weight and are subject to lower shear forces from the wind?

I believe that in all cases the answer is the same. Elephants.

During the last interglacial period in Britain (the Eemian stage, that ran from 130,000 to 113,000 years ago) and in southern Europe until about 30,000 years ago, our ecosystems were dominated by the straight-tusked elephant, Elephas antiquus. It was a monster, built on such a scale that it made the African elephant look like a ballet dancer. Its great neck suggests that it specialised in ripping trees to bits. Any edible tree unable to hedge or coppice would have been wiped out. Black and white bark might have confused an animal with limited colour vision, much as a zebra’s coat bamboozles predators. Understorey trees that, even when mature, are small enough for monstrous elephants to reach their crowns need be fantastically strong to survive.

The climate during the Eemian was similar to our own. Britain then contained much of our familiar wildlife, living alongside monsters. When Trafalgar Square was excavated in the 19th Century, the river gravels were found to be stuffed with bones. Most of the large ones belonged to hippos: Hippopotamus amphibius, the same species that still lives in Africa. The diggers also found the remains of elephants, rhinos, giant deer, aurochs, hyaenas and lions. (Yes, there were lions in Trafalgar Square, long before Sir Edwin Landseer got to work). In other words, like almost everywhere on earth, both on land and at sea, we had a megafauna. Megafaunas are the default state of most ecosystems. That they are now confined to a few pockets in Africa and Asia appears to be the result of hunting and habitat wreckage by humans. Wherever we go, we walk in the shadows of the past.

Why does blackthorn put out vicious spines two or three inches long when it has been cut or flailed? They appear to be wildly overengineered to resist browsing by deer or cattle, but not perhaps by rhinoceros. Why are there so many marginal species: plants that live on the edges of ponds and rivers? Could it be because they evolved to use the niches created by wallowing hippos, aurochs and wild boar? Why are robins so tame in Britain, but not on the Continent? Perhaps because the robin is to the wild boar what the oxpecker is to the Cape buffalo. In the absence of boar, they have chosen the next best thing: for them, we are simply fake pigs. Ours is a ghost ecosystem, adapted to species that no longer live here.

...

Top Predators

Account of reintroduction of top predators in various parts of the world - not just the Yellowstone wolves - and discussion of the pro and cons of interfering with top predator / mesopredator relationships.

Status and Ecological Effects of the World’s Largest Carnivores,
ScienceMag,
[link]

Large carnivores face serious threats and are experiencing massive declines in their populations and geographic ranges around the world. We highlight how these threats have affected the conservation status and ecological functioning of the 31 largest mammalian carnivores on Earth. Consistent with theory, empirical studies increasingly show that large carnivores have substantial effects on the structure and function of diverse ecosystems. Significant cascading trophic interactions, mediated by their prey or sympatric mesopredators, arise when some of these carnivores are extirpated from or repatriated to ecosystems. Unexpected effects of trophic cascades on various taxa and processes include changes to bird, mammal, invertebrate, and herpetofauna abundance or richness; subsidies to scavengers; altered disease dynamics; carbon sequestration; modified stream morphology; and crop damage. Promoting tolerance and coexistence with large carnivores is a crucial societal challenge that will ultimately determine the fate of Earth’s largest carnivores and all that depends upon them, including humans.

... reintroducing wolves to their former home range across the American West is a major benefit to wildlife and healthy habitats. It is also essential. All this article says is that the results are not as quick or simple as some environmentalists want to believe:

Perhaps you’ve seen one of these videoclips: the scene opens up of wolves galloping in the snow, then landscapes of rivers and mountains opening up before you. Pictures of deer and elk, bears, bison, beavers, badgers, foxes, eagles, and so on, are paraded before us to beautiful music. They are all told to be living again in harmony and balance, thanks to one factor: wolves. You hear the exalted voice of George Monbiot saying things like “Birds began to return to the park!” and “But this is where it gets truly remarkable, it turns out that reintroduction of wolves even changes the course of rivers!”

Large predators are an important part of upholding the balance of ecosystems, for sure. But does an ecosystem “miraculously” return back to normal, including its physical landscape, by introduction of one of its main predators, 70 years after its removal?

Uplifting videos, like the ones produced by the Sustainable Human and the National Geographic, certainly do a good job convincing us that this is what has in fact happened. They are truly lovely (if a tad melodramatic) stories, too. But I think they would be better if they were accurate.

Devon Beavers

After a 400-year absence, the industrious rodents are back. On a river near Okehampton their reintroduction has led to biodiversity and cleaner water

The Devon project targets three key indicators: water storage, flood attenuation and water quality. The beavers are, they believe, helping in all three. The 13 dams they have built along the 150 metres stretch of water have increased water storage capacity, evened out the flow of water and improved the quality of the water that emerges from the dams.

Research was undertaken at the Devon Beaver Project, a controlled reintroduction programme in South West England.

In early spring 2011, a pair of Eurasian beavers was introduced to a three-hectare enclosure – roughly the same as 4.5 football pitches – on a stream in the headwaters of the River Tamar. Their activity on the site, according to the report from the University of Exeter, has “created a complex wetland environment, dominated by ponds, dams and an extensive canal network.”

This, in turn, has led to benefits including:

Increased water storage within the site and a reduction in water flow out of it. This is due to the way the beavers have engineered the environment. The report says “this is highly likely for the observed attenuating impact upon flood flows across a range of storm event sizes”.

The full report is called Eurasian beaver activity increases water storage, attenuates flow and mitigates diffuse pollution from intensively-managed grasslands and can be seen on the sciencedirect website.

Beavers in wooded site, on first order tributary draining from agricultural land.

Beaver activity has resulted in major changes to ecosystem structure at the site.

Beaver activity increased water storage within site and attenuated flow.

Reduced sediment, N and P, but more DOC in water leaving site.

Important implications for nature based solutions to catchment management issues.

Abstract

Beavers are the archetypal keystone species, which can profoundly alter ecosystem structure and function through their ecosystem engineering activity, most notably the building of dams. This can have a major impact upon water resource management, flow regimes and water quality. Previous research has predominantly focused on the activities of North American beaver (Castor canadensis) located in very different environments, to the intensive lowland agricultural landscapes of the United Kingdom and elsewhere in Europe.

Two Eurasian beavers (Castor fiber) were introduced to a wooded site, situated on a first order tributary, draining from intensively managed grassland. The site was monitored to understand impacts upon water storage, flow regimes and water quality. Results indicated that beaver activity, primarily via the creation of 13 dams, has increased water storage within the site (holding ca. 1000 m3 in beaver ponds) and beavers were likely to have had a significant flow attenuation impact, as determined from peak discharges (mean 30 ± 19% reduction), total discharges (mean 34 ± 9% reduction) and peak rainfall to peak discharge lag times (mean 29 ± 21% increase) during storm events. Event monitoring of water entering and leaving the site showed lower concentrations of suspended sediment, nitrogen and phosphate leaving the site (e.g. for suspended sediment; average entering site: 112 ± 72 mg l− 1, average leaving site: 39 ± 37 mg l− 1). Combined with attenuated flows, this resulted in lower diffuse pollutant loads in water downstream. Conversely, dissolved organic carbon concentrations and loads downstream were higher. These observed changes are argued to be directly attributable to beaver activity at the site which has created a diverse wetland environment, reducing downstream hydrological connectivity. Results have important implications for beaver reintroduction programs which may provide nature based solutions to the catchment-scale water resource management issues that are faced in agricultural landscapes.

It has previously been asserted that baleen whales compete with fisheries by consuming potentially harvestable marine resources. The regularly applied “surplus-yield model” suggests that whale prey becomes available to fisheries if whales are removed, and has been presented as a justification for whaling. However, recent findings indicate that whales enhance ecosystem productivity by defecating iron that stimulates primary productivity in iron-limited waters. While juvenile whales and whales that are pregnant or lactating retain iron for growth and milk production, nonbreeding adult whales defecate most of the iron they consume. Here, we modify the surplus-yield model to incorporate iron defecation. After modeling a simplistic trajectory of blue whale recovery to historical abundances, the traditional surplus-yield model predicts that 1011 kg of carbon yr−1 would become unavailable to fisheries. However, this ignores the nutrient recycling role of whales. Our model suggests the population of blue whales would defecate 3 × 106 kg of iron yr−1, which would stimulate primary production equivalent to that required to support prey consumption by the blue whale population. Thus, modifying the surplus-yield model to include iron defecation indicates that blue whales do not render marine resources unavailable to fisheries. By defecating iron-rich feces, blue whales promote Southern Ocean productivity, rather than reducing fishery yields.

Whales facilitate carbon absorption in two ways. On the one hand, their movements — especially when diving — tend to push nutrients from the bottom of the ocean to the surface, where they feed the phytoplankton and other marine flora that suck in carbon, as well as fish and other smaller animals. The other ... is by producing fecal plumes. “In other words, pooing,” ... “That also introduces nutrients that create marine plants in the area. These plants use photosynthesis, which absorbs carbon, thus enhancing the carbon capture process.”

But as waters steadily grow warmer, whales may not be able to survive in the region. It’s difficult to predict just how climate change will affect the species, said Barefoot, because they’re part of a complicated ecosystem with many interlinked species.

One Whale Is Worth Thousands of Trees in Climate Fight By Jana Randow, Bloomberg, November 20, 2019
[link]

Climate activists would be better off trying to save whales rather than planting trees if they had to choose between those options, according to a study published by the International Monetary Fund.

Great whales are the carbon-capture titans of the animal world, absorbing an average of 33 tons of CO2 each throughout their lives before their carcasses sink to the bottom of the ocean and remain there for centuries, according an article in the December issue of the IMF’s Finance & Development magazine. A tree, by contrast, absorbs no more than 48 pounds of the gas a year.

That difference prompted Ralph Chami and Sena Oztosun from the IMF’s Institute for Capacity Development, and two professors, Thomas Cosimano and Connel Fullenkamp, to argue that supporting international efforts to restore whale populations -- decimated to 1.3 million by years of industrialized hunting -- “could lead to a breakthrough in the fight against climate change.”

“Coordinating the economics of whale protection must rise to the top of the global community’s climate agenda,” they wrote. “Since the role of whales is irreplaceable in mitigating and building resilience to climate change, their survival should be integrated into the objectives of the 190 countries that in 2015 signed the Paris Agreement for combating climate risk.”

In addition to binding significant amounts of CO2 themselves, whales also support the production of phytoplankton, which contributes at least 50% of all oxygen to the Earth’s atmosphere and captures as much CO2 as 1.7 trillion trees, or four Amazon forests.

Increasing phytoplankton productivity by just 1% would have the same effect as the sudden appearance of 2 billion mature trees, according to the study.

Protecting whales and raising their numbers comes at a cost. The authors put the value of one animal at more than $2 million, taking into account the value of carbon sequestered over the whale’s lifetime as well as other economic contributions such as fishery enhancement and ecotourism.

The researchers argue that if the whale population were allowed to grow to around 4 to 5 million -- the total before the era of whaling -- thereby capturing 1.7 billion tons of CO2 annually, it would be worth about $13 per person per year in subsidies.

International financial institutions would be “ideally suited to advise, monitor, and coordinate” actions of individual countries, the authors said.

Artificial reefs / subway cars

Simon Thorrold, a scientist in the biology department at Woods Hole Oceanographic Institute, told mental_floss, “There is no doubt that if you put subway cars into areas with little hard structure, they will attract invertebrates, and then they will attract fish.”

But it’s hard to know whether that additional habitat is increasing fish populations or just moving them around, “The question is: Are you increasing productivity? Or just aggregating fish that are [already] there?" Thorrold says. "If it's the latter, you just make the fish easier to catch. Which is not necessarily bad, but you can't claim that the reef is adding fish."

Abstract
Natural climate solutions (NCS) in the Arctic hold the potential to be implemented at a scale able to substantially affect the global climate. The strong feedbacks between carbon-rich permafrost, climate and herbivory suggest an NCS consisting of reverting the current wet/moist moss and shrub-dominated tundra and the sparse forest–tundra ecotone to grassland through a guild of large herbivores. Grassland-dominated systems might delay permafrost thaw and reduce carbon emissions—especially in Yedoma regions, while increasing carbon capture through increased productivity and grass and forb deep root systems. Here we review the environmental context of megafaunal ecological engineering in the Arctic; explore the mechanisms through which it can help mitigate climate change; and estimate its potential—based on bison and horse, with the aim of evaluating the feasibility of generating an ecosystem shift that is economically viable in terms of carbon benefits and of sufficient scale to play a significant role in global climate change mitigation. Assuming a megafaunal-driven ecosystem shift we find support for a megafauna-based arctic NCS yielding substantial income in carbon markets. However, scaling up such projects to have a significant effect on the global climate is challenging given the large number of animals required over a short period of time. A first-cut business plan is presented based on practical information—costs and infrastructure—from Pleistocene Park (northeastern Yakutia, Russia). A 10 yr experimental phase incorporating three separate introductions of herds of approximately 1000 individuals each is costed at US$114 million, with potential returns of approximately 0.3–0.4% yr−1 towards the end of the period, and greater than 1% yr−1 after it. Institutional friction and the potential role of new technologies in the reintroductions are discussed.